In the Claisen rearrangement of allyl phenyl ether, what is the major organic product formed?

• A. $C_6{H}_5\mathrm{OH}$ (phenol)
• B. o-allylphenol
• C. p-allylphenol
• D. benzyl alcohol

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the Claisen rearrangement mechanism, which is a [3,3]-sigmatropic rearrangement involving allyl aryl ethers. The reaction proceeds through a cyclic six-membered transition state, leading to the migration of the allyl group to the ortho or para position relative to the oxygen atom on the aromatic ring.
2. Step 2: Identify the starting material, allyl phenyl ether, which consists of a phenyl ring bonded to an oxygen atom that is also connected to an allyl group (–CH2–CH=CH2).
3. Step 3: Recognize that the Claisen rearrangement typically favors formation of the ortho-substituted product due to the proximity of the allyl group to the ortho position, allowing the cyclic transition state to form more easily and with less steric hindrance.
4. Step 4: Draw the product structures for both ortho-allylphenol and para-allylphenol to compare. The ortho product has the allyl group adjacent to the hydroxyl group on the benzene ring, while the para product has it opposite the hydroxyl group.
5. Step 5: Conclude that the major product is o-allylphenol (ortho-allylphenol) because the Claisen rearrangement proceeds through a six-membered cyclic transition state that favors substitution at the ortho position relative to the phenol oxygen.